Preparation of organopolysiloxanes



densed hydroxyl groups attached to the silicon.

ven as the SiOH linkages.

United States Patent PREPARATION OF ORGAN OPOLYSILOXANES John J. Duane, Kenmore, N. Y., assignor to Union Carllfidekand Carbon Corporation, a corporation of New No Drawing. Application June 22, 1951, Serial No. 233,121

14 Claims. (Cl. 260-4482) The invention is concerned with the making of organopolysiloxanes (commonly called silicones) and more particularly it consists in an improved process for condensing or polymerizing silanols to higher polymeric siloxane products.

Organosilanols are the intermediate products in the preparation of silicones. They have the representative structure R1Sl(0H)4z, where R is alkyl, aryl, or other organic radical capable of direct union with the silicon atom, and x is a number not exceeding 3. Silanols result from the hydrolysis of corresponding halogenosilanes, or other hydrolyzable silane derivatives, and they in turn condense, or can be caused to condense, to form the characteristic SiO-Si bond structure of the polysiloxanes. The ease with which the silanols condense is dependent in large part upon the nature of the organic radical or radicals attached to the silicon atom in the monosilane starting compound, and while condensation to varying degrees often occurs almost simultaneously with the hydrolysis, the usual product from the hydrolyzing step is either a complete silanol derivative, or a partially condensed siloxane containing a high proportion of uncon- In either instance further condensation must then be efiected in order to obtain the higher molecular weight siloxane polymers, and in prior practice the accomplishment of this, with end results at all uniform, has been attained only with considerable difiiculty.

It is an object of this invention to provide means for controlling more readily and accurately the condensation of organosilanols, in order to obtain siloxane polymers more consistent and uniform in molecular structure and size.

In accordance with the invention the intermediate silanol product from a chlorosilane or other silane hydrolysis is further condensed in the presence of an anhydrous potassium salt of a weak acid, with other conditions being controlled, particularly as to temperature and pressure, so that Water of condensation is permitted to escape from the reaction zone. Anhydrous potassium carbonate is especially efltective as a condensing agent, and substantially similar results have been obtained with condensation in the presence of other dry, normal potassium salts of weak acids, such, for example, as potassium bicarbonate, potassium cyanide, or potassium phosphate.

The function of the potassium salt in this reaction is very specific, in its ability to condense SiOH units in the molecule without affecting the essential SiO Si bonding of the siloxane structure, or linkages like SiOR or SiH, which are often desirable in the final polymer product. It also appears that this unique action is specific only to the anhydrous potassium salts of the kind mentioned, as attempts to efi'ect similar results with sodium carbonate have been quite unsuccessful, and, as is well known, compounds like potassium and sodium hydroxides effect polymerization by action on SiOfiSi bonds as The latter condensing.

-barely pourable oil.

I Patented May 8, 1956 ice I V 2 agents also attack SiOR bonds, and quantitatively break up any SiH units which may be present.

The process of the invention is widely applicable in furthering the condensation of hydrolysis products from a variety of silane starting materials and mixtures thereof, and this is additionally illustrated in the following examples, showing first the condensation of pure silanol materials, and then'the process as applied sequentially with the hydrolyzing step in a polymenforming reaction.

Example 1 A sample of high purity crystalline diethylsilanediol, (C2Hs)2Si(OH)2, was heated with anhydrous potassium carbonate for one and a half hours, under about 5 mm. pressure and at maximum temperature of 140 C. A very viscous oil was obtained, showing a condensation, or polymerization, well beyond that which normally occurs under the same conditions without the presence of potassium carbonate.

Example 2 A mixture of 4 gram moles of diethylsilaned'iol, (C2H5)2Si(OH)2, and 1 gram mole of diphenylsilanediol, (CsH5)2Si(OH)2, was heated with anhydrous potassium carbonate for one hour, to a temperature of C. under about 5 mm. pressure. A very heavy oil resulted, showing a viscosity of 14,500 centistokes at 100 F. From the solubility characteristics of this oil, there was clear indication that copolymerization took place, as well as a quite complete condensation of all hydroxyl units.

Example 3 Diethyldichlorosilane was hydrolyzed by adding 7 moles of this silane to a suspension of 1500 grams of sodium bicarbonate in a solvent mixture of 1250 cc. of ether and 250 cc. of acetone. This method of hydrolyzing is described in further detail in my copending application Serial No. 133,689, filed December 17, 1949. The product, after filtering and removing solvent, was largely low molecular weight diethylsilanols, such as diethylsilanediol and the linear trimer and tetramer homologues. The uncondensedhydroxyl content was 9.2%, which lies be tween the similar values for the trimer and tetrarner. Extraction with water showed that the monomeric diol was present, but only in small amounts. One.hundred grams of this product was refluxed at about 5 mm. pressure in the presence of 5 grams of potassium carbonate. At the end of 25 minutes, the temperature had reached C., and an increase in viscosity was evident. After heating an additional hour and a half at about 5 mm. pressure, the polymer was scarcely pourable. The product was dissolved in ether, washed, dried, and then concentrated to a clear, extremely viscous oil.

Example 4 Diethyldichlorosilane in an amount of 4 moles was hydrolyzed in 3000 cc. of acetone with 900 grams of sodium bicarbonate. After filtering and removing the solvent, the hydrolysis product was heated under about 5 mm. pressure for 3 hours with 25 grams of potassium carbonate, the maximum temperature being C. The resulting polymer was so elastic that it could be pulled out through the neck of the flask in one piece. The elastomer flowed under influence of gravity and was soluble in ether. A substantially complete polymerization appeared to have been attained in this product.

A second experiment similar to the above was made except that the hydrolyzate was heated for only two hours with potassium carbonate. The resultant polymer was a Example 5 I Diphenyldichlorosilane was hydrolyzed by the sodium slurried in 3000. cclof acetone.

13 bicarbonate technique 'of the two above examples, giving a nearly 'white crystalline product comprised mo'stly'bf diphenylsilanediol. A portion of the latter was heated v.undervacuum withrpotassium carbonate to 180-". C.,. and

a solid, dilatant, thermoplasticur esin wasobtained.

.-. Example 6 Ethyltrichlorosilane was hydrolyzed iri.the presence of sodium'bicarbonateto yield avery viscous oil. This oil, in amount of 0.13 gram mole; .-was'.dissolved in acetone together with 0.32 mole,diethylsilanedioland 0.08 mole diphenylsilanediol. The. solution was warmed .-with grams of potassium carbonate, under 5 mm. pressure at 25 C. for 30 minutes,while acetone was removed. The potassiumcarbonatebecame hydrated and S grams more -.were.--added. After furtheraheating to 140 C., it was necessary to tdecantcthez light .oil.onto. additional dry .potassium. carbonate, and heating was then continued -for another 30minutes, reacl1ing a.--temperature of 90 C. Thefinal product was a: gel which was clearlywindicated to -be-.ofi acopolymer .composition.

Example 7 Six gram moles ofdiethyldichlorosilane and 1 gram mole-of trimethylchlorosilane weretaddedto a slurry of 21400. grams of sodium bicarbonate: in a-mixture of 1 liter .ofetherrand ahalf liter.of.acetone. Under these. condi- ,tions,. linear silanols. aresformed :ratheri-than .the cyclic polymers. *The hydrolyzed .residue .was refluxed at -140." C. and 5mm. pressurezfor .15:hours,'.in the presence iof l0.grams 50f potassium carbonate. :Theviscosity of "the: product-was .401 centistokes-at 100 F.,' and the Example 8 Three gram'moles ofdiethyldichlorosilane and 1 gram mole-of trimethylchlorosilane were a'dded slowly to 800 grams of sodium bicarbonate slurried in 3000 cc. of acetone. The slurry was-dried-over calcium sulfate and filteredQ Tothe' filtrate 5 grams-of KzCOs'Were added, and the solvent was removedunder vacuum. '-Some condens-ation tookplace withrelease of water sufiicient to dissolve the potassium carbonate. The-light oil 'was separated and refluxed 'with S-grams more of potassium "carbonate'under 5 pressure. After minutes the temperature had reached '60" C.,"'and the inadequate "amount -of KzCOa was hydrated. This :oil" was .again decanted-onto 5 grams of fresh anhydrous K'aCOa, and heated, withprovisionfor removing the water evolved from' therefiux condenser to prevent hydration of the After an hour and a half at 125. C., 72% of the polymer was recovered. The'oil product had a .viscosity of 104 centistokes' at 100 F.,-a'nd the silanol content was less than 0.1%.

.In a. second similar experiment, 3 grarrrmoles of diethyldichlorosilane and ahalf mole oftrimethylchlorosilane wereadded 50.800, grams of..sodiurn.bicarbonate Inthis run considerably more potassium v-carbonatewas .used, and .onheating the .water evolved .was removedas it. entered the reflux con- .denser. After 2. hours at a temperature reaching a maxi mum of 135- C., under 5 mm; pressure, 19% 'of-polymer .was;recovered,-. with a viscosity-.of 364. centistokes at 100 F.,' and asilanol contentlof-less than 0.1%.

The-two .experiments'of Example 8;. as :well as Example 6,-show theirnportanceof conducting the reaction so as to prevent hydration; of the potassium carbonate; inorder .-to. obtain more 1 eifective -.control of; the polymerization.

1 {This isrillustrated" in theyfollowing: threeuexamples.

Example 9 One mole of ethylethoxy dichlorosilane,

(C2H5 Si( OCzHs C12 Example 10 Two hundred grams of a mixture containing 3 parts of ethylethoxy dichlorosilane and 1 part of diethyl dichlorosilane were. co-hydrolyzed,. using 300-grams of sodium bicarbonate'in='500 ccnofiwacetone. 'The de- .solvated hydrolyzate, a silanol with theuinitial ethoxy grouping intact, was heated. at .C. under atmospheric pressure for two and a half hours innthe presence of 3grams*of:potassium carbonate. A thick-oily-polymer resulted, vwhichnby: analysis :was'found still to retain the .Si-OR grouping.

- Example 11 By the same bicarbonate hydrolysis techniquealready described, a hydrolyzate was prepared fromv a 1mixture .of 2.moles of diethyldichlorosilane, 1- mole-of-:diphenyldichlorosilane, and 1 mole. of phenylethoxy dichlorosilane. This silanol mixture was treated with 5.. grams .of potassium carbonate: at atmospheric pressure for 1 hour: at "v C.,.and the oilypolymen resulting was :againrfound to have the initial. ethoxy grouping intact.

' Example 12 Inorder to'test the effect of weak acid potassium'salts other than the carbonate, experiments were made using -as the added -s-alt potassium bicarbonate, potassium cyanide and potassium phosphate. 'ried out byheating SO-grams ofdiethyl silan'ediol with These-tests were car- 5 grams of the respectivedry-potassium salts,"at' about 125 C. and under about 5mm. of mercury pressure. The products, dissolved in ether," were Washed with water to removethesalLseparated from 'the water and dried with calcium-sulfate. After stripping'oif the ether under vacuum at-l00 C.,'oils of varying viscosity were obtairied. "There is clear indication that with suitable, and slight, alterations in temperature, salt concentrations, or other reaction conditions, the viscosity, or extent of polymerization, in the final product can be quite readily. controlled.

In allof'the above examples the hydrolysis step described is one using the sodium bicarbonate technique, which has-proven to have many advantages, but other, and older, ways of hydrolyzing, such as the ether-ice -method, can be appropriate, while still utilizing the improved condensing reaction of'this invention. Usually certain heating isdesirable to promote the'reaction, but with somestartingmaterials, particularly such as the trifunctional silane: derivatives, which "condense'more readilythan-others, effective polymerization can-'be obtained at substantially atmospheric temperatures. Anhydrous potassium. carbonate is. a' preferred condensing agent,.but, as indicated, other .wealc acidisalts ofpotassium are considered similarly etfective. Operation under'vacunm is a convenient. means for1maintaining substantially anhydrous conditions invthereaction zone, but other ways of accomplishing this,..such. as by.nitrogen sparging can also'be used.

.The. wide. applicabilityof the. process so tar as the .starting silane. materials are concerned; has been-well illus- .trated, and .many. variations 1 in actual-operational steps may be possible within the broad intent of the invention.

I claim:

1. In the making of organ-opolysiloxanes by hydrolysis of a hydrolyzable organosilane taken from the group consisting of hydrocarbon and hydrocarbonoxysilanes with subsequent condensation, the improvement which comprises condensing the intermediate hydrolysis product in contact with a substantially anhydrous potassium salt of a weak inorganic acid, while providing for removal of water of condensation from the reaction zone.

2. In the making of organopolysiloxanes by hydrolysis of a hydrolyzable organosilane taken from the group consisting of hydrocarbon and hydrocarbonoxysilanes with subsequent condensation, the improvement which comprises condensing the intermediate hydrolysis product in contact with substantially anhydrous potassium carbonate, while providing for removal of water of condensation from the reaction zone.

3. In the making of organopolysiloxanes by hydrolysis of an organohalosilane taken from the group consisting of hydrocarbonhalosilane and hydrocarbonoxyhalosilanes with subsequent condensation, the improvement which comprises heating the intermediate hydrolysis product of said organohalosilane in the presence of anhydrous potassium carbonate, while maintaining reduced pressure and a temperature sufficient to provide for removal of water of condensation from the reaction zone.

4. in the making of orgauopolysiloxanes by hydrolysis of an organohalosilane taken from the group consisting of hydrocarbonhalosilane and hydrocarbonoxyhalosilanes with subsequent condensation, the improvement which comprises heating the intermediate hydrolysis product of said organohalosilane in the presence of anhydrous potassium cyanide, while maintaining reduced pressure and a temperature sufiicient to provide for removal of water of condensation from the reaction zone.

5. A process for preparing organopolysiloxanes which comprises reacting an organohalosilane taken from the group consisting of hydrocarbonhalosilanes and hydrocarbonoxyhalosilanes, with sodium bicarbonate under substantially anhydrous conditions to produce silanol compounds and condensing said silanol compounds by contacting therewith a substantially anhydrous potassium salt of a weak inorganic acid while providing for the removal of Water of condensation from the reaction zone.

6. A process for preparing an organopolysiloxane' which comprises reacting an organohalosilane taken from the group consisting of hydrocarbonhalosilanes and hydrocarbonoxyhalosilanes with sodium bicarbonate, under substantially anhydrous conditions to produce silanol compounds and condensing said silanol compounds by heating said silanol compounds while in contact with anhydrous potassium carbonate under reduced pressure and at a temperature sufiicient to provide for the removal of water of condensation from the reaction zone.

7. A process for preparing organopolysiloxanes which comprises reacting a mixture of diethyldichlorosilane and trimethylchlorosilane with sodium bicarbonate, under substantially anhydrous conditions, to produce silanol compounds and condensing said silanol compounds to a viscous oil by heating said silanol compounds, while in contact with anhydrous potassium carbonate, to a reflux temperature under reduced pressure.

8. A process of condensing organosilanols having the formula RzSi (OH) 4-:

wherein R is an organic radical taken from the group consisting of hydrocarbon radicals and hydrocarbonoxy radicals and x is an integer from 1 to 3, to polyorganosiloxanes which comprises heating said organosilanols in the presence of a substantially anhydrous potassium salt of a weak inorganic acid, while providing for the removal of water of condensation from the reaction zone.

9. A process of condensing organosilanols having the formula wherein R is an organic radical taken from the group consisting of hydrocarbon radicals and hydrocarbonoxy radicals and x is an integer from 1 to 3, to polyorganosiloxanes which comprises heating said organosilanols in the presence of substantially anhydrous potassium carbonate, while providing for the removal of water of condensation from the reaction zone.

formula RzSi(0H)4-x wherein R is an organic radical taken from the group consisting of hydrocarbon radicals and hydrocarbonoxy radicals and x is an integer from '1 tof3, to polyorganosiloxanes which comprises heating said organosilanols in thepresence of substantially anhydrouspotassium cyanide, while providing for the removal of water of condensation from the reaction zone.

11. A process of condensing organosilanols having the formula R1Si(OH)4-e wherein R is a hydrocarbon radical and x is an integer from 1 to 3, to polyorganosiloxanes which comprises heating said organosilanols in the presence of a substantially anhydrous potassium salt of a weak inorganic acid, while providing for the removal of water of condensation from the reaction zone.

12. A process of condensing organosilanols having the formula RzSi(OH) 4-:

wherein R is an alkyl radical and x is an integer from 1 to 3, to polyorganosiloxanes which comprises heating said organosilanols in the presence of a substantially anhydrous potassium salt of a weak inorganic acid, while providingfor the removal of water of condensation from the reaction zone.

13. A process of condensing organosilanols having the formula Rx Si(OH)4-x I wherein R is an aryl radical and x is an integer from 1 to 3, to polyorganosiloxanes which comprises heating said organosilanols in the presence of a substantially anhydrous potassium salt of a weak inorganic acid, while providing for the removal of water of condensation from the reaction zone.

14. A process of condensing organosilanols having the formula (R') I( )IS [4- -11 wherein R is a hydrocarbon radical, R is a hydrocarbonoxy radical, x is an integer of from 1 to 3, y is an integer of from 0 to 2 and x+y is not greater than 3, which comprises heating said organosilanols in the presence of a substantially anhydrous potassium salt of a weak inorganic acid, while providing for the removal of water of condensation from the reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,218 Rochow Oct. 7, 1941 2,395,550 Iler Feb. 26, 1946 2,426,912 Wright Sept. 2, 1947 2,449,572 Welsh Sept. 21, 1948 2,457,539 Elliot et al Dec. 28, 1948 2,482,276 Hyde et a1. Sept. 20, 1949 2,590,812 Barry Mar. 25, 1952 2,646,441

10. A process of condensing organosilanols having the Duane July 21, 1953 

1. IN THE MAKING OF ORGANOPOLYSILOXANES BY HYDROLYSIS OF A HYDROLYZABLE ORGANOSILANE TAKEN FROM THE GROUP CONSISTING OF HYDROCARBON AND HYDROCARBONOXYSILANES WITH SYBSEQUENT CONDENSATION, THE IMPROVEMENT WHICH COMPRISES CONDENSING THE INTERMEDIATE HYDROLYSIS PRODUCT IN CONTACT WITH A SUBSTANTIALLY ANHYDROUS POTASSIUM SALT OF A WEAK INORGANIC ACID, WHILE PROVIDING FOR REMOVAL OF WATER OF CONDENSATION FROM THE REACTION ZONE. 